An audience measurement system typically includes one or more device meters to monitor the media presented by one or more media devices located at one or more monitored sites. Such a device meter can use watermarks decoded from the presented media and/or signatures (also referred to as media fingerprints) generated from the presented media, or both, to monitor (e.g., identify and/or track) the media being presented by a media device. For example, identification codes, such as watermarks, ancillary codes, etc., may be transmitted within media signals. Identification codes are data that are transmitted with media (e.g., inserted into the audio, video, or metadata stream of media) to uniquely identify broadcasters and/or media (e.g., content or advertisements), and/or are associated with the media for another purpose such as tuning (e.g., packet identifier headers (“PIDs”) used for digital broadcasting). Codes are typically extracted using a decoding operation.
In contrast, signatures are a representation of some characteristic of the media signal (e.g., a characteristic of the frequency spectrum of the signal). Signatures can be thought of as fingerprints. They are typically not dependent upon insertion of identification codes in the media, but instead preferably reflect an inherent characteristic of the media and/or the signal transporting the media. Systems to utilize codes and/or signatures for audience measurement are long known. See, for example, Thomas, U.S. Pat. No. 5,481,294, which is hereby incorporated by reference in its entirety.
When signatures are used for media monitoring, signatures of the monitored media (referred to herein as collected signatures or site signatures) are generated by the device meter and compared to reference signatures representative of reference media known to the audience measurement system. In prior audience measurement systems, the device meters typically provide their generated site signatures to a data processing facility or other centralized processing site for comparison with the reference signatures that are representative of the possible reference media available for consumption at the respective monitored sites. Such comparison may involve comparing large numbers of site signatures with large numbers of reference signatures, especially when the number of monitored sites is large and/or the amount of possible reference media available for consumption is large.
Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts, elements, etc.